Dejan Ivezić

New approach to milling circuit control—robust inverse Nyquist array design

The aim of this paper is to present an application of robust inverse Nyquist array control design method to a milling circuit in Majdanpek Copper Mine. An existent model of a milling circuit was adopted to respond to robust inverse Nyquist array methodology demand by introducing model uncertainty, and optimal robust controller of milling circuit is designed. The proposed controller is robust for reference signals. The robustness of multivariable feedback systems with designed controller is tested and compared with different, previously designed multivariable controllers. Simulation results, in time domain, demonstrate the preferable performance of the designed robust controller in setpoint tracking. Implementation of the new controller without any investments in new equipment significantly improves performance of the milling process.

The Potential of and Barriers to Renewable Energy Sources in Serbia

Serbia is heavily dependent on expensive imported energy resources (oil, gas, and high-quality coal) that place a big burden on the economy. Pollution, related to energy production and consumption, is becoming a great environmental concern in the country. At the same time, it is estimated that Serbia has the potential to produce almost 4 Mtoes per year from renewable energy sources. It is more than half of current primary energy production. In this regard, renewable energy resources appear to be one of the most efficient and effective solutions for clean and sustainable energy development. This article presents the potentials of renewable energy sources in Serbia and key barriers for their development and utilization.

The state and perspective of the natural gas sector in Serbia

ABSTRACT The strategy of long-term energy development of Serbia identifies an increase of share of natural gas in final energy consumption as one of the main aims. Serbia has signed a strategic agreement with the Russian Federation on cooperation in the oil and gas sector, within which the project South Stream pipeline is planned to be realized. In addition, the Republic of Serbia has signed the Treaty that establishes the Energy Community and accepted the obligation to implement the Energy Community acquis. In the natural gas sector it is related to establishing a fully liberated national and regional natural gas market. Overview and analysis of the current state concerning indigenous production, infrastructure, and consumption structure are presented as the basis for projections of the possible Serbian natural gas sector development. Three possible scenarios for future natural gas consumption, considering different influential parameters, have been developed by the Long-range Energy Alternatives Planning System (LEAP) software. Scenarios characterized by different levels and structures of consumption are analyzed in detail.

Availability as a dimension of energy security in the Republic of Serbia

There is a range of modern approaches and models in literature for the evaluation and determination of energy security, which are based on different parameters and indicators. For most of them, a common characteristic is emphasizing the availability of energy, as an important dimension for ensuring energy security. In this paper, concise overview of Serbian energy sectors is given and appropriate energy indicators are defined and determined. Selected indicators provide insight into the main components that characterize availability – security of supply, self-sufficiency, diversification of energy sources, the level of renewable energy use, and technological maturity. Besides calculation of energy indicators, the aim is to investigate and establish the relationships among components of availability of energy in Republic of Serbia, and to provide some recommendations for the policy makers to develop efficacious measures for enhancing energy security. Therefore, analytic hierarchy process methodology is applied to analyse collected data, to reveal cause – effect relationships, and to prioritize components of availability mutually. Conclusion is that the main activities in Serbian energy sector should be directed to improvement of energy efficiency, increase the use of renewable energy sources and diversification of energy sources and energy imports directions.

Effect of natural gas composition on methane number: A case of gas reservoirs in Serbia

ABSTRACT Natural gas is considered as the most environmentally acceptable fossil fuel, thus it is an alternative to petroleum derivate, dominantly used in internal combustion engines. Physical properties of a fuel as well as behavior during combustion process are affected by its composition. This article presents analysis of effect of natural gas composition on methane number (MN), conducted for natural gas deposits in Serbia. For empirically determination of MN: California air resources board (CARB) method and Linear and Anstalt für Verbrennungskraftmaschinen list (AVL) method have been applied. Effect of reactive hydrogen and carbon ratio, Wobbe index and content of inert matter on MN is discussed. For compositions characterized with total share of inert compounds higher than 5%, impact of inert components becomes significant, without observed dependency between reactive hydrogen and carbon and MN. An analysis has shown that carbon dioxide and nitrogen have differently affect MN. Carbon dioxide affects the increase of MN due to higher molar specific heat, appearance of dissociation, and higher activation energy.

Framework for biomass project selection at local level — the case study

Biomass is individually the most significant renewable resource potential in Serbia, but this energy source is still far from being sufficiently and adequately utilized. Biomass energy utilization generally depends on a large number of factors, as its availability, cost-effectiveness, level of biomass market development, economic incentives, infrastructure development, etc. Most of these factors are related to local (municipalities) level. Therefore, the framework for mapping municipal spatial, infrastructural, resource related and logistic prerequisites for electricity and/or heat generation from biomass, and selecting of biomass projects is proposed in this paper. The methodology is applied to Srem District, which is diverse in biomass potentials ranging from agriculture and farm biomass to forestry biomass. Evaluation of biomass potential of Srem District is given and three projects of biomass utilization are proposed for further elaboration.

Study of Dependability Evaluation for Multi-hierarchical Systems Based on Max–Min Composition

This article presents the model for calculating the performance of dependability for complex technical systems. According to ISO-IEC 300, dependability is an overall indicator for the quality of service and considers simultaneously reliability, maintainability, and maintenance support. For a proper understanding of the quality of service for any technical system, it is important to define dependability performance at the level of single component as well as at the upper levels—levels of subsystems and entire system. As dependability indicators (reliability, maintainability, and maintenance support) have been defined as linguistic variables, the fuzzy max–min composition has been used for the dependability determination and integration of its indicators. A procedure for the synthesis of single components dependability performance to upper levels in complex technical system is proposed. Max–min composition is again used as a tool for fuzzy synthesis because it enables obtaining the comprehensive and synergetic effect in a process of dependability evaluation. A practical engineering example (mechanical systems at bucket wheel excavator) has been used to demonstrate the proposed dependability synthesis model. Copyright

Research and development of efficient, environmentally improved household gas appliances

An experimental research and analysis of performance of three domestic house hold gas appliances was carried out. The objective of this work, based on the conducted analysis of the research data, was to improve the appliances’ performance, prefer ably through relative simple modifications, in order to satisfy DIN 4702 emissions and efficiency standards when using different fuels, including natural gas, liquefied petroleum gases and lower quality natural gas. This report summarizes details of this work and how the objectives were achieved. .